1. Field of the Invention
The present invention relates to a measuring system, and more particularly, to a measuring system capable of contacting a node with a probe to measure characteristics of a signal on the node precisely, and filtering the signal to a specific frequency range in which the signal is required to be measured through a plurality of capacitors, to display information of amplitude vs. frequency of the signal on a frequency analyzer.
2. Description of the Prior Art
With the improvement of technology, electronic products are all desired to be of smaller size and higher performance nowadays, such that density of elements distributed on a circuit board keeps increasing, and circuit areas shrink substantially. However, when the circuit areas become smaller, more and more elements are crowded into a small space, which causes higher interferences between each other. Among the interferences, an electromagnetic interference (EMI) is one of the problems most troublesome in the industry. Since EMI is concerned with many factors and needs a wider range of professional knowledge to be solved, it has confused design engineers of electronic systems for a long time. However, under higher competition in the high technology electronic industry and shorter life cycle of new products, how to solve EMI rapidly becomes a challenge for all electronic engineers.
A conventional measuring system 10 for measuring EMI can be referred to FIG. 1. The measuring system 10 includes a frequency analyzer 104 and a probe 106, utilized for measuring EMI on a circuit board 102. The circuit board 102 includes electronic elements E1˜E3 and nodes N1˜N6, wherein the electronic elements E1˜E3 are connected to each other through the nodes N1˜N6 and circuits. Structure of the probe 106 is shown in FIG. 2. The probe 106 includes a circular terminal 202, a line 204, and an output interface 206. When EMI on the node N1 needs to be measured, the circular terminal 202 can be placed near the node N1 to measure EMI signal dissipated from the node N1. Then, the signal is transmitted to the frequency analyzer 104 through the line 204 and the output interface 206, and information of amplitude vs. frequency of the signal is displayed on the frequency analyzer 104.
However, each node N1˜N6 on the circuit board 102 may dissipate EMI signals. When measuring the EMI signal on the node N1 with the conventional EMI measurement method, the circular terminal 202 may also receive electromagnetic signals dissipated from the other nodes N2˜N6. The nodes N2˜N6 closer to the circular terminal 202 have a higher probability of causing a measurement error, so as to affect the measurement result. Moreover, when excess EMI on the circuit board 102 is known, and from which node or element on the circuit board 102 the excess EMI is generated needs to be determined, the conventional EMI measurement method with the circular terminal 202 may not achieve accurate results.
Besides, almost all of the main advanced countries in the world define a standard for electromagnetic compatibility (EMC) and EMI of electronic devices. The current mainstream standard for EMI falls within the frequency range 30 MHz˜1 GHz, wherein the energy of an EMI signal is required to be lower than a specific value. However, in order to meet each kind of requirement, the frequency analyzer 104 always provides a greater frequency range for measurement (e.g. 3 MHz˜3 GHz), and can not provide measurement results more accurately for a specific requirement in a specific frequency range. Thus, there is a need for improvement of the prior art.